In order to obtain resins having low specific gravity, namely, light weight, and having flexibility and high mechanical strength, a technique of using crosslinked foams has been widely used for building interior and exterior materials, automobile parts, such as interior trim and door glass run, packaging materials, daily necessaries, etc. The reason is that since mere foaming of resins induces lowering of mechanical strength, molecular chains are bonded by the crosslinking reaction of the resins to make it possible to attain lightening due to foaming with inhibiting lowering of mechanical strength.
Also for footwear and footwear parts, such as shoe soles (mainly midsoles) of sport shoes, crosslinked foams of resins have been used, and the reason is that there have been desired materials which are lightweight, are inhibited from deformation due to long-term use and have mechanical strength to endure severe use conditions and vibration-damping properties to absorb impact in the landing.
For the shoe soles, a crosslinked foam of an ethylene/vinyl acetate copolymer has been heretofore used and widely known. The crosslinked foam obtained by molding a composition of the ethylene/vinyl acetate copolymer has a high specific gravity and a high compression set, and therefore, when it is used for shoe soles, there arise problems that the shoe soles are heavy and they are compressed by the long-term use and thereby lose mechanical strength.
In National Publication of International Patent No. 501447/1997 and Japanese Patent Laid-Open Publication No. 206406/1999, an invention relating to a crosslinked foam using an ethylene/α-olefin copolymer and an invention relating to a crosslinked foam using a mixture of an ethylene/vinyl acetate copolymer and an ethylene/α-olefin copolymer are described, respectively. In these inventions, the low specific gravity and the compression set properties have been improved, but satisfactory performance has not been obtained yet (patent documents 1 and 2).
In Japanese Patent Laid-Open Publication No. 277539/2003, an invention relating to a foam having excellent flexibility is described. The foam described in this invention, however, is inferior in vibration-damping properties in the temperature range in the vicinity of body temperature, in said temperature range shoe soles (mainly midsoles) of sport shoes being used, and is inferior in mechanical strength because the foam is attended with no crosslinking reaction. In WO2005/000958, an invention relating to a foam having excellent flexibility is described. However, further improvement in vibration-damping properties at room temperature to high temperatures has been desired (patent documents 3 and 4).
In order to solve the above problems, the present inventors have earnestly studied, and as a result, they have found that a foam of excellent vibration-damping properties is obtained by adopting a resin composition comprising an ethylene/α-olefin copolymer (A) and a hydrogenated copolymer (B) obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, or further a resin composition comprising an ethylene/α-olefin copolymer (A), a hydrogenated copolymer (B) obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, and a natural resin such as a rosin-based or terpene-based resin or a petroleum resin (C), or further a resin composition comprising an ethylene/α-olefin copolymer (A), a hydrogenated copolymer (B) obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, a natural resin such as a rosin-based or terpene-based resin or a petroleum resin (C) and an ethylene/polar monomer copolymer (D). Based on the finding, the present invention has been accomplished.
Patent document 1: National Publication of International Patent No. 501447/1997
Patent document 2: Japanese Patent Laid-Open Publication No. 206406/1999
Patent document 3: Japanese Patent Laid-Open Publication No. 277539/2003
Patent document 4: International Patent Publication WO2005/00958